The present invention relates to a process for preparing adsorptive porous resin beads and to a method of recovering an organic material from a fluid stream by passing the fluid stream containing the organic material over the adsorptive resin beads.
Organic materials, mainly organic solvents are commonly used in industrial processes. During their use they are often contacted and diluted with air, water or other fluid streams. Recovering such organic materials from the fluid streams is highly desirable in order to avoid environmental problems and in many cases also to recover valuable organic materials which can be reused.
Activated carbon is frequently used for recovering organic materials such as hydrocarbons and halogenated hydrocarbons. Typically, a gas stream, such as air containing such organic materials, is passed through a filter bed containing activated carbon. When the activated carbon is loaded with the hydrocarbons or halogenated hydrocarbons, the activated carbon is regenerated with steam at an elevated temperature. This method has substantial disadvantages. Some halogenated hydrocarbons are cracked in the presence of water and heat. The produced acid such as hydrochloric acid causes severe corrosion problems The steam used for regeneration of activated carbon will become contaminated with the hydrocarbons and has to be purified after the regeneration step Furthermore, the combination of activated carbon, water and heat often destroys the stabilizer which has been added to the halogenated hydrocarbon.
Much research efforts have been spent on the production of cross-linked polymers, typically in the shape of resin beads, for various applications. Some of the cross-linked polymers have been suggested in methods of recovering organic materials from fluid streams
Well-known cross-linked polymers are polymers of a vinyl aromatic monomer such as styrene or alphamethylstyrene which are cross-linked with a an oligovinylbenzene such as divinylbenzene or trivinylbenzene.
U.S. Pat. No. 3,686,827 suggests the use of alkylstyrene polymers which are cross-linked with divinyl benzene for removing an organic vapor such as gasoline vapors, methylene chloride or trichloroethylene.
German Offenlegungsschr.frt DE-A-2 027 065 (equivalent to U.S. Pat. No. 3,727,379) suggests the use of polymers of styrene and 2 to 80 weight percent divinylbenzene containing polar groups for removing impurities from gases. The impurities are for example SO.sub.2, mercaptans, aromatic, saturated or unsaturated hydrocarbons, alcohols, ethers or amines. The polymers contain halogen, nitro, hydroxyl, ester, aldehyde, keto, amide, nitrile or methylol groups.
U.S. Pat. No. 4,358,546 describes a crosslinked copolymer of chloromethylstyrene and divinylbenzene having from 9.0 to 17.0 mole percent divinylbenzene.
U.S. Pat. No. 3,822,244 describes a process for the cross-linking of polystyrene by chloromethylating the benzene rings of the polystyrene macromolecule followed by methane bridge cross-linking resulting from dehydrochlorination, all carried out in the presence of a nonsolvent for polystyrene (being a solvent for the chloromethyl ether) and a Friedel-Crafts catalyst.
In order to increase the porosity and the adsorbent properties of the aromatic polymer beads people skilled in the art have suggested to prepare slightly cross-linked aromatic polymer beads and to post-cross-link them in the presence of a Friedel-Crafts catalyst.
U.S. Pat. No. 4,263,407 discloses polymeric adsorbents which are of the macronet type and their use for recovering organic solvents from gaseous streams. The macronet type adsorbents are prepared from lightly cross-linked macroreticular (macroporous) beads of polystyrene or a copolymer of styrene and divinylbenzene which have been externally post-cross-linked with a polyfunctional alkylating or acylating agent in the presence of a Friedel-Crafts catalyst. The resins disclosed require the use of the additional external cross-linking agent and exhibit swellability characteristics which result in a loss of physical stability and increased fouling A similar method of adding additional cross-linking is described in U.S. Pat. No. 3,729,457 wherein linking bridges are provided by bisfunctional benzyl compounds.
U.S. Pat. Nos. 4,191,813 and 4,192,920 disclose polymeric adsorbents prepared from lightly cross-linked copolymer beads of vinylbenzyl chloride. The lightly cross-linked copolymer beads are post-crosslinked in the presence of a Friedel-Crafts catalyst. Polymeric adsorbent beads of the macronet type are obtained. The same use of the beads is described as in U.S. Pat. No. 4,263,407. The resins are very expensive to prepare due to the high cost of vinylbenzyl chloride.
U.S. Pat. No. 2,629,710 discloses halomethylated styrene polymers cross-linked with 0.5 to 8 percent divinylbenzene. The cross-linked styrene/divinylbenzene copolymers are halomethylated by treatment with chloromethyl ether and a Fridel-Crafts catalyst. During the step of halomethylation, some cross-linking by the halomethylating agent can take place. The halomethylated beads are converted to ion exchange resin beads by reaction with trimethylamine gas. Some of the produced ion exchange resins containing quaternary ammonium groups are highly porous and are useful for adsorbing penicillin.
European Patent Application 152780 discloses a method for increasing the porosity of cross-linked copolymers of mono- and polyvinyl aromatic compounds. The method involves contacting aromatic cross-linked copolymer beads having no halomethyl groups with a Lewis acid catalyst in the presence of an organic solvent. European Patent Application 152780 suggests to use the disclosed resins for removing cephalosporin C from an acidic aqueous solution.
Due to the insufficient physical stability, high protection costs or insufficient (dynamic) capacities of many of these polymeric materials, most of these polymeric materials are not commercially used in methods of recovering organic materials such as halogenated hydrocarbons from fluid streams such as air or water.
DD-A-249,703 discloses a process for producing porous polymeric adsorbents having a surface area of 800 to 1,600 m.sup.2/ g. In DD-A-249,703 many of the above mentioned teachings are discussed. The inventors of DD patent 249,703 have tried to overcome the deficiencies of the polymeric beads disclosed in the above mentioned teachings. According to their teaching the polymeric adsorbents are prepared by polymerization of styrene and divinylbenzene whereby the copolymer is cross-linked in such a manner that its amount of cross-linking agent is 2 to 8 weight percent divinylbenzene. Chloromethyl groups are then introduced into the copolymer such that the degree of substitution of chloromethyl groups is greater than 0 4 (11.5 percent Cl). The copolymer is washed with an organic solvent, the solvent is removed and the cross-linked polystyrenes are swollen in a halogen-containing hydrocarbon. The swollen copolymers are post-cross-linked in the presence of a Friedel-Crafts catalyst After the end of the reaction the chlorinated hydrocarbon is removed from the product and the product is made hydrophilic. The produced post-cross-linked polymer beads are characterized by a good water absorbance.
As an alternative to the disclosed process, DD-A-249,703 suggests chloromethylating an unfunctionalized cross-linked styrene/divinylbenzene copolymer having 2 to 8 weight percent divinylbenzene and cross-linking the chloromethylated copolymer as described above in a single pot.
DD-A-249,703 mentions that the adsorbent resins produced according to the described process are suitable for adsorbing gaseous, liquid or dissolved solids and are useful for solving waste water, separation and purification problems in the chemical industry.
DD-A-249,274 discloses the same adsorbent resins and the same process for preparing them as DD-A-249,703 The adsorbent beads must be made hydrophilic. DD-A-249,274 discloses the use of the resins for removing harmful materials such as toxins and urea-bonding substances from the body liquids of patients with functional failure of the kidneys or liver.
DD-A-249,l94 and DD-A-249,l93 suggest the use of hydrophilic adsorbent resins for removing aliphatic, aromatic and/or chlorinated hydrocarbons from hydrogen chloride gas. The hydrophilic adsorbent resins have an inner surface of 800 to 1,600 m.sup.2/ g. The adsorbent resins are produced by a "special" post-cross-linking of styrene/divinylbenzene copolymers. Neither DD-A-249,l94 nor DD-A-249,l93 teach how to carry out such a post-cross-linking. "Wofatit Y77" is mentioned as an example of the adsorbent resins. The exhausted beads are desorbed with steam. However, desorption with steam has the above mentioned disadvantages. Some halogenated hydrocarbons are cracked in the presence of water and heat. The produced acid such as hydrochloric acid causes severe corrosion problems The steam used for regeneration purposes will become contaminated with the hydrocarbons and has to be purified after the regeneration step. The purification of the steam does not cause any substantial problems when water-immiscible halocarbons or halogenated hydrocarbons are adsorbed by the resins, however, the main problem connected with waste water purification is caused by those organic materials which are soluble in or miscible with water.
Furthermore, hydrophilic adsorptive resin beads such as those mentioned in DD-A-249,l94 and DD-A-249,l93 and such as those disclosed in DD-A-249,703 and DD-A-249,274 only have a limited use for recovering an organic material from fluid streams such as water or air. When recovering organic materials from water, hydrophilic adsorbent resins also adsorb water which decreases the adsorbent capacity of the resins for the organic material. Furthermore, the hydrophilic resins tend to swell in water which decreases their adsorbent capacity per volume of resin The adsorption of water also renders the desorption step more difficult. Furthermore, it is very often desired to recover waterless organic materials such as waterless halogenated hydrocarbons from the resins in the desorption step in order to avoid an additional separation step Also when recovering organic materials from air it is undesirable that the adsorbent resins adsorb water vapor from humid air. Some halogenated hydrocarbons are cracked in the presence of water when increasing the temperature in the desorption step. Accordingly, it would be desirable to provide a new process for preparing adsorptive porous resin beads which are useful in a method of recovering an organic material from a fluid stream.